Citations are used to avoid plagiarism. It's not a difficult task; just a tedious one. However, it's better than failing an assignment or getting sued over something so easily done.
Direct quotes, paraphrasing, and summarizing are all things that should be cited. It doesn't matter what it's from, book, movies, tv shows, even music. If it's another authors work, then it needs a citation.
Direct quotes are when you take someone else's exact words. If it's two words or a paragraph, either way it needs a citation. These need to be used as least as possible.
Paraphrasing is when you take a quote or section from a writer and rewrite it in your own words. This is a great way to shorten up a section or make it fit in better with your writing. These should be used as least as possible as well.
Summarizing is a brief explanation of something. You want to cut to the point as much as possible keeping it mostly the authors main ideas. This is not the time to state your own ideas or opinions.
Patchwork is the result if you do use direct quotes and paraphrasing too often. Soon it starts to be a paper with 12 different authors work. You need to remember to include your opinions and reasonings.